There has been proposed a digital audio disc having recorded thereon audio signals in the form of pulse-coded signals with a series of pits, which will be optically read, for example, to reproduce the recorded audio signals. Unlike conventional phonographic records, most digital audio discs available are "one-sided", having only one information-recorded surface (hereinafter referred to as a "face") with the opposite non-information-recorded surface (hereinafter referred to as a "back") bearing a label which indicates the titles of recorded music pieces and other data. It is therefore possible for an operator to place such a digital audio disc to be played back with the face and back inverted inadvertently into an optical disc player which will reproduce audio signals from the digital audio disc. When the operator commits such an error, the disc player cannot be brought into a playback starting condition, that is, a state of normal preliminary focusing operation unless the operator finds the error in disc loading, although the disc player initiates a preliminary focus control as a usual operation in preparation for playing back the disc. In the event of such an error, therefore, the preliminary focus control is repeated in the disc player through a process which is wasteful and renders the disc player ineffective. Besides, the repeated wasteful process tends to become a source of malfunctions of the disc player.
One proposed way of determining whether the disc is loaded properly or not on the disc player is to employ optical detecting means for discriminating the face from the back of the disc, in addition to an optical pickup means for reading the pits formed on the disc. In such a case, the optical detecting means emits a detecting beam of light to the disc and detects a beam of light reflected from the disc. Since the back of the disc is formed into an unreflecting surface bearing a label or otherwise processed, no or little light is reflected from the back of the disc upon exposure to the detecting light beam and therefore the disc player is arranged, so that a disc placed therein is detected as being improperly loaded in position when no or little light is reflected, and otherwise determined as being properly loaded.
The above discrimination system is disadvantageous in that it is not always able to discriminate accurately the face of a disc from the back thereof as backs of discs of different kinds may have different light reflectivities, respectively.